Heat exchangers including flat tubes and fins have been known in the art. Patent Documents 1 and 2 show heat exchangers of this type. Specifically, in each of the heat exchangers of Documents 1 and 2, laterally extending flat tubes are arranged to be spaced from one another in the vertical direction (i.e., the upward and downward directions) by a predetermined distance, and plate-like fins are arranged to be spaced from one another by a predetermined distance in the direction in which the flat tubes extend. For example, as illustrated in FIG. 2 of Patent Document 2, in the heat exchanger of this document, slender notches are formed in the fins, and the flat tubes are inserted in these notches. In this heat exchanger, air flowing between the fins exchanges heat with fluid flowing in the flat tubes.
In general, fins in heat exchangers of this type are provided with heat transfer promotion parts, e.g., bent-out parts, for promoting heat transfer of air between the fins. In the fins illustrated in FIGS. 3 and 13 of Patent Document 1 and FIG. 2 of Patent Document 2, a plurality of bent-out parts are arranged side by side in the air passage direction.